The present invention relates generally to over-voltage protection circuits suitable and, more particularly, to over-voltage protection of analog functional modules.
Analog functional modules, for example, an analog-to-digital converter (ADC) of a system on chip (SOC) device sometimes need to handle input voltages that exceed the voltage rating of the devices constituting the analog functional module. One known way of handling high analog input voltage ranges on a SOC incorporating devices with a lower rating employs a resistor divider network connected at the front end of the analog module. However, the resistor divider network constitutes a continuous load on the input, which results in inefficiency as, in the particular example of a multi-channel ADC, one of the channels may be idle for some considerable time. Cutting-off the continuous loading of the divider network can overcome the inefficiency problem. However, in so doing, the functional module may see a high voltage at its input, which can affect reliability. Using comparatively high resistor values for the divider network will reduce the loading but, disadvantageously, increase RC time delays in the input path.
Hence it would be advantageous to provide a front-end circuit that can eliminate input loading without the drawbacks of the known arrangements while also providing input over-voltage protection.